1. Field of the Invention
The invention relates to implantable heart stimulators such as implantable cardiac pacemakers or implantable cardioverters/defibrillators (ICDs). In particular, the invention refers to implantable heart stimulators that comprise means for intracardiac impedance monitoring and for wireless transmission of data.
2. Description of the Related Art
Implantable medical devices comprising a telemetry unit for data communication with an external device allow for a data exchange between the implantable medical device and a central service center via the external device. Thus, the implantable medical device (implantable pacemaker or ICD) can transmit its operation parameters and physiological parameters measured e.g. by intracardiac or epicardial electrodes to the central service center where the data can be evaluated and a physician can be informed in case of any event needing a physician's assistance. By means of a wireless data transmission from the implantable medical device via the external device to the central service center a continuous monitoring of a patient is possible without the need for time consuming visits at the physician's premises.
Systems for such remote monitoring of patients are for example disclosed in U.S. Pat. No. 6,434,429, U.S. Pat. No. 6,470,215, U.S. Pat. No. 6,544,171 and U.S. Pat. No. 6,553,262.
The parameters to be monitored include a patient's heart rhythm, preferably both the atrial rhythm and the ventricular rhythm, the patients physical activity by means of hemodynamic sensor, therapeutic events such as atrial or ventricular stimulation pulses or defibrillation shocks triggered by the implantable medical device and intracardiac impedance.
It is also known to use intracardiac impedance for controlling the stimulation rate in a close loop stimulation system (CLS) as it is disclosed in U.S. Pat. No. 6,263,243.